1. Field of the Invention
The present invention relates to a shift Control Apparatus for a speed change apparatus (transmission), especially for a synchromesh type transmission.
2. Related Art
In a synchromesh-type transmission, as shown in FIG. 5, sleeves 17 and 18 which constitute a part of a cynchro mechanisms 15 and 16 are pressed to one of free-rotate gear groups of a 2nd-shift gear 11, a 3rd-shift gear 12 and a 4th-shift gear 13 (a 1st-shift gear and the like are not shown) mounted onto an output shaft 30 disposed coaxial with an input shaft 10, thereby rotating the free-rotate gear together with the output shaft 30. On a counter shaft 40 disposed parallel to the output shaft 30, gears 41, 42 and 43 are mounted to mesh with the above gears 11, 12 and 13 respectively.
The above synchromesh transmission is mainly comprised of clutch hubs 21 and 22, sleeves 17 and 18, second speed to fourth speed gear pieces 23 to 25, three synchronize rings 27 to 29. In detail, the clutch hubs 21 and 22 are spline-engaged with the input shaft 10 to be rotated together therewith, and the sleeves 17 and 18 are engaged with an outer peripheral surface of the clutch hubs 21 and 22 via splines 17a and 18a to be shifted axially but not to be rotated circumferantially relative thereto. Each of the second-speed gear piece 23, the third-speed gear piece 24 and the fourth-speed gear piece 25 is spline-engaged with a boss portion protruded from a side face of the free-rotate gear and having on an outer periphery thereof a dog teeth 23a, 24a and 25a. The synchronize rings (hereinafter, briefly called "ring") 27, 28 and 29 for second-speed, the third shft and the fourth shift are disposed respectively between a cone surface of the gear pieces 23, 24 or 25 and splines 17a and 18a on the inner peripheral surfaces of the sleeves 17 and 18.
Between the clutch hub 21 and the sleeve 17, and between the clutch hub 22 and the sleeve 18, shift keys (not shown) are respectively mounted by engaging with axial grooves formed by cutting some parts on the outer periphery of the clutch hubs 21 and 22 and nipped by inner peripheral surfaces of the sleeve 17 and 18. The shift gear has radial protrusions which engage with recesses formed on the inner peripheral surface of the sleeve 17 or 18 positioned at the neutral position, and disengage from the sleeve 17 and 18 positioned other than the neutral position.
Shift forks 31 and 32 engage with the sleeves 17 and 18, respectively. One of the shift forks 31 and 32 is engaged by a select member (not shown) selectively moved by a select operation of an operate (manual) lever in a select direction, then the selected sleeve 17 or 18 is moved (shifted) by a shift operation of the operate lever in a shift (Y) direction.
A speed-change process of the above synchromesh-type transmission will be explained with reference to FIG. 6 which shows a shift/select pattern of the operate lever, FIG. 7 which shows a stroke position of the sleeves 17 and 18, and FIG. 8 which shows an operate pressure of an actuator which actuates the sleeves.
In the synchromesh-type transmission, as shown in FIG. 5, the select member is engaged with the shift fork 31 in the 2nd-speed condition prior to the speed-change, and the sleeve 17 of the synchro mechanism 15 is shifted leftwardly. To the contrary, the sleeve 18 of the synchro mechanism 16 is positioned in the nuetral position. For speed-changing from a 2nd shift to a 3rd shift, as shown in FIG. 6, the operate lever is shifted from a 2nd shift position to a nuetral position N, then selected from a position corresponding to a 1st shift and 2nd shift to a position corresponding to a 3rd shift and a 4th shift, and then shifted from the neutral position N to a 3rd shift position.
When the operate lever is shifted from the 2nd shift position to the neutral position N at the time T1 in FIG. 7, an operate force directed rightwardly in FIG. 5 is applied to the sleeve 17 via the select member and shift fork 31, so that the sleeve 17 slides over the gear piece 23 of the 2nd-shift gear 11 without recieving resistance to reach the neutral position N at the time T2. This time period (T.sub.1 -T.sub.2) is called a "shift draw-out area").
After the shift draw-out of the sleeve 17, the operate lever is operated in the select direction so that the select member is disengaged from the shift lever 31 and is engaged with the shift lever 32 during a time period (T.sub.2 -T.sub.3) of FIG. 7. The shift fork 32, by a successive shift operation of the operate lever, starts to shift the sleeve 18 of the synchro mechanism 16 rightwardly in FIG. 5 at a time T.sub.3. As a result, the shift key, by cooperating with the sleeve 18, presses an end surface of the ring 28. A time period (T.sub.3 -T.sub.4) when the shift key presses the end surface of the ring 28 is called a "shift push-in (index) area".
As apparent from FIG. 7, the sleeve 17 shifts by a constant speed in the shift draw-out area (T.sub.1 -T.sub.2), and the sleeve 18 shifts by a constant speed in the shift push-in area (T.sub.3 -T.sub.4) but is stopped in the select area (T.sub.2 -T.sub.3).
At a time T.sub.4 when the shift key does not follow the shift of the sleeve 18, a chamfer of the spline 18a of the sleeve 18 starts to engage with outer teeth 28a of the ring 28. A stroke position of the sleeve 18 corresponding to the time T.sub.4 is called a "synchronize start point (balk point)" where the sleeve 18 is stopped irrespective the force applied thereto. In the stroke position S of the balk point T.sub.4, the sleeve 18 presses the ring 28 against the gear piece 24 and waits time T.sub.5 when the gear piece 24 synchronizes with the sleeve 18 and the ring 28 of low-speed rotation. This time period (T.sub.4 -T.sub.5) is called a "synchronize area" where the sleeve 18 is stopped.
When the gear piece 24 synchronize with the sleeve 18 and the ring 28, a rotation friction torque between the ring 28 and the gear piece 24 is removed, so that sleeve 18 as the shifting thereof pushes apart the ring 28 and meshes with the dog teeth 24a of the gear piece 24. At this time, the rotate speed of the gear piece 24 and the 3rd-shift gear 12 is decreased to a value smaller than that upon the synchronization with the sleeve 18 due to drag torque thereof. For this reason, upon a re-synchronizing when the sleeve 18 meshes with the dog teeth 24a of the gear piece 24, the load applied from the gear piece 24 and the 3rd-shift gear 13 to the sleeve 18 varies suddenly. This stroke position of the sleeve 18 is called "two-shift input point".
The sleeve 18, after having pushed apart the gear piece 24 by overcoming the load at the two-shift input point, receives a stop force from an end surface of the 3rd-shift gear 12 to stop at a stroke position corresponding to a time T6. This time period (T.sub.5 -T.sub.6) is called "push-apart area" in which the sleeve 18 shifts in a constant speed. Thereafter, the sleeve 18 is maintained at the 3rd-shift position by a predetermined lock mechanism which engages with the shift fork 32 and the operate lever.
The shifting of the sleeves 17 and 18 of the synchro-mechanisms 15 and 16 based on the shift operation of the shift lever is automatically operated by a hydraulic or electric actuator controlled by a controller. One of the transmission which includes such automatic operation is shown in WO97/05410, for example. In this prior art, as shown in FIG. 8, a control means including the controller, adjusts an operate pressure of the actuator based on a vehicle condition or a speed-change process.
In detail, the control means sets an operate pressure in a max. value P.sub.max in the shift draw-out area (T.sub.1 -T.sub.2) of the sleeve 17 and the shift push-in area (T.sub.3 -T.sub.4) of the sleeve 18 to shift the sleeves 17 and 18 by a large drive force and in a high speed. On the other hand, at the balk point where the synchronization of the sleeve 18 with the ring 28 etc. are started, the operate pressure of the actuator is decreased to an adjusted value P.sub.1 needed for the synchronizing to thereby press the sleeve 18 against the ring 28 by a weaker force. Such weaker press force is convenient to extend an endurance character of construction members of the transmission and to reduce or prevent a noise or a speed change shock occurred upon the synchronizing. In a push-apart area (T.sub.5 -T.sub.6) after a time T.sub.5 when the synchronization has been completed and a predetermined time period after having detected a stop point, the operate pressure for the actuator is set in the max. value P.sub.max again to shift the sleeve 18 by the large force and in the high speed. In a time period before the speed-change operation and a time period after the stop point, the operate pressure of the actuator is set in zero.
However, in the conventional control manner by the control means for the actuator, the operate pressure of the actuator is maintained in the max. value during the shift draw-out area (T.sub.1 -T.sub.2) of the sleeve 17, select area and the shift push-in area (T.sub.3 -T.sub.4) of the sleeve 18, and maintained in the max. value at the balk point B where the sleeve 18 starts to synchronize with the ring 28. Therefore, the sleeve 18 abuts against the ring 28 by the large drive force and in the high speed to thereby generate the speed-change shock and the noise. If the operate pressure of the actuator upon the shifting push-in of the sleeve 18 is decreased, there is fear that the shift push-in of the sleeve 18 may become inaccurate or longer time is required for the shift push-in of the sleeve 18. On the other hand, the operate pressure of the actuator is adjusted (decreased) to the adjusted value P.sub.1 to thereby decrease the drive force of the sleeve 18 correspondingly. However, the speed-change shock or noise may be generated even in this adjusted value P.sub.1 depending on the rotate speed of the gear piece 24 and the like.
In addition to the speed change from the 2nd shift to the 3rd shift via the select operation, in a speed change from the 4th shift to the 5th shift via a select operation and a shift-down operation via the select operation, the speed-change shock or the noise may occur. Same problem may occur in a speed change (shift-up and shift-down) without the select operation. That is, the shock/noise may occur in all kinds of the shift operation.